This invention is directed to crystalline (R),(S)-.alpha.-pivaloyloxyethyl-(S)-3-(3,4-dihydroxyphenyl)-2-methylalani nate also referred to herein as "diastereomeric L-.alpha.-methyldopa POE ester" (wherein .alpha.-pivaloyloxyethyl is abreviated POE and (S)-3-(3,4-dihydroxyphenyl)-2-methylalanine is referred to by its more common name L-.alpha.-methyldopa), and a process for its isolation from a crude reaction mixture.
The diastereomeric mixture of (R)- and (S)-isomers of L-.alpha.-methyldopa POE ester is a known antihypertensive compound of Formula (I), see Saari et al., U.S. Pat. No. 3,983,138, which is herein incorporated by reference. ##STR1##